Treebeard, Gracious Host, Spike Feeder, and Xenograft

Prerequisites

• Treebeard, Gracious Host on the battlefield
• Spike Feeder on the battlefield
• Xenograft on the battlefield
• Spike Feeder has at least one +1/+1 counter on it
• "Halfling" or "Treefolk" chosen with Xenograft

Steps

1. Activate Spike Feeder's second ability by removing a +1/+1 counter from it, causing you to gain two life
2. Treebeard triggers, putting two +1/+1 counters on Spike Feeder
3. Repeat
4. Once Spike Feeder has infinite +1/+1 counters, you may target any other creature with Treebeard's ability

Results

• Infinite +1/+1 counters
• Infinite lifegain
• Infinite lifegain triggers